The invention relates to an apparatus at a spinning preparation machine, especially at a flat card, roller card or the like, in which a clothed, rapidly rotating roller lies opposite to at least one clothed and/or non-clothed component and the spacing between the components lying opposite to one another is changeable.
In flat cards, crashes occur that are caused by incorrect settings or incorrect machine operation. The repair costs for such crashes are considerable. The result of even any slight contact between a stationary component and, for example, a carding cylinder, is destructive because, in the event of contact, the roller clothing strongly takes hold of the components because of its aggressive tooth setting and, when contact is identified, for example by an operator, the rollers run on for at least five minutes until they come to a standstill. During that time the damage becomes ever greater.
The effective spacing of the tips of a clothing from a machine element lying opposite to the clothing is called the carding nip. The last-mentioned element may also have a clothing but could, instead of that, be formed by a segment of a circuit having a conductive face. The carding nip determines the carding quality. The size (width) of the carding nip is an important machine parameter that shapes both the technology (fibre processing) and the running behaviour of the machine. The carding nip is set as narrow as possible (it is measured in tenths of a millimeter) without the risk of a “collision” of the working elements being incurred. In order to ensure uniform processing of the fibres, the nip needs to be as identical as possible over the whole of the working width of the machine.
The carding nip is affected especially by the machine settings on the one hand and by the condition of the clothing on the other hand. The most important carding nip of the revolving card top flat card is located in the main carding zone, that is to say between the cylinder and the revolving card top assembly. At least one clothing that limits the working spacing of the carding zone as a whole is in motion, usually both. In order to increase the production rate of the flat card, it is sought to select an operating rotational speed, or an operating speed of the moving parts, that is as high as the fibre processing technology allows. The working spacing changes in dependence on the operating conditions. The change occurs in the radial direction (starting from the rotational axis) of the cylinder.
During carding, increasingly large amounts of fibre material are processed per unit of time, which requires higher working component speeds and higher installed outputs. The increasing throughput of fibre material (production rate), even when the working surface area remains constant, results in increased generation of heat as a result of the mechanical work. At the same time, however, the technological carding result (sliver uniformity, degree of cleaning, nep reduction etc.) is constantly being improved, which requires a greater number of effective surfaces in carding engagement and narrower settings of those effective surfaces with respect to the cylinder (tambour). The proportion of synthetic fibres being processed, which—compared with cotton—generate more heat as a result of friction when in contact with the effective surfaces of the machine, is continually increasing. The working components of high-performance flat cards are nowadays totally enclosed on all sides in order to conform to the high safety standards, to prevent the emission of particles into the spinning room environment and to minimise the need for servicing of the machines. Grids or even open, material-guiding surfaces allowing exchange of air are a thing of the past. The said circumstances markedly increase the input of heat into the machine, while the discharge of heat by means of convection is markedly reduced. The resulting more intense heating of high-performance flat cards leads to greater thermoelastic deformation which, on account of the non-uniform distribution of the temperature field, affects the set spacings of the effective surfaces: the gaps between cylinder and card top, doffer, fixed card flats and take-off stations with blades are reduced. In an extreme case, the set gap between the effective surfaces can be completely consumed by thermal expansion, so that components moving relative to one another collide, resulting in considerable damage to the affected high-performance flat card. Accordingly, particularly the generation of heat in the working region of the flat card can lead to different degrees of thermal expansion when the temperature differences between the components are too great.
In order to reduce or avoid the risk of collisions, the carding nip between clothings lying opposite to one another is in practice set relatively wide, that is to say a certain safety spacing exists, but a large carding nip results in undesired nep formation in the card sliver. On the other hand, an optimum, especially narrow, dimension, by means of which the nep occurrence in the card sliver is appreciably reduced, is desirable.
It is an aim of the invention to provide an apparatus of the type described at the outset that avoids or mitigates the mentioned disadvantages and, especially, when opposite-lying components draw near to one another, avoids contact between those components in a simple manner.